docs: def _check_expiration(self, url: str, data: 'SavedEndpoint') -> 'SavedEndpoint':
          """Checks the expiration time for data for a url.
  
          If the data has expired, it is deleted from the cache.
  
          Args:
              url: url to check
              data: page of data for that url
  
          Returns:
              value of either the passed data or None if it expired
          """
          if data.expires_after < time.time():
              del self.data[url]
              data = None
          return data